Echo ranging and listening gear



EhQTO /l NI H. M. TRENT ETAL ECHO HANGING AND LISTENING GEAR Filed July 31, 1944 Feb. 1, 1949.

QQ K Patented Feb. 1,,1949

ECHO HANGING AND LISTENING GEAR Horace M. Trent and Thomas F. Jones, Alexandria, Va.

Application July 31, 1944, Serial No. 547,470 9 Clalms. (Cl. 177-386) (Granted under the act of March a, 1883, as

amended April 30, 1928; 370 0. G. 157) The present invention relates in general to systems for underwater echo ranging, directionindicating and listening.

An important object of the invention is the provision of a sytem of the above type capable of embodiment in a battery operated, light weight,

compact readily portable form, for operation from small patrol vessels for locating and maintaining sound contact with a submerged target.

Another object is to provide a device capable of use for the location of submarines by direct audio listening; super audio listening or by echo ranging.

Another object is the provision of a simplified electronic,'automatic keying system.

A further object is the reduction of interference from reverberation.

Various other objects and advantages of the in- A of the Rochelle salt type and in the well known" manner may be housed in a thin metal casing and designed for use with either over-the-side, or sound-well training gear. The training gear, indicated diagrammatically at H, may be of any known or other suitable form capable of rotating the transducer in a horizonal plane, and although not so indicated, may be also tiltable.

There are two physical operating links between the receiver and transmitting portions, first a control of the connection of the transducer to the receiver through a normally closed contact 12 on a relay l3 in the transmitter circuit, and second a time-variable-gain control of the receiver from the transmitter by way of a voltage divider R--48 and condenser C-22 in a manner and for a purpose to be later described.

Referring now to the diagram more in detail, and first to the receiver portion on the lower part of the. drawing, this comprises aninput transformer Tl having its primary connected through normally closed contact l2 to the transducer l0 and its secondary connected with the input of the first of a pair of amplifier tubes Vl and V-2 connected in cascade. The amplifiers feed into a duplex-diode trlode V-3 for detection and amplification in the case of supersonic reception. A push-pull amplifier tube V-4 receives the audio output from the amplifier section of the duplex diode through a push-pull transformer T-2 and passes it on amplified through a pushpull transformer T3 and output jack J-l to a headset or other suitable receiving device not shown. A local oscillator-tube V-5 rendered effective by closure of switch S4 supplies local oscillations to the input diode electrodes of tube V3 for beat frequency reception when desired.

A'change from one to the other adaptation of the receiver .to reception of audio or superaudio frequency waves, is provided for through the use of a change-over switch 8-5 here shown in the position for reception of audio frequencies. This switch may be of any known or other suitable form such as the type having several contact segments mounted on a common shaft for movement in unison as indicated conventionally in the drawing by the dotted lines connecting the fine arcuate sections.

Audio reception-For reception of signals at audio frequencies the local oscillator control switch S--@ is opened and the switch 8-5 is set as shown with its indicating handle in the solid line position indicated at AF. This connects the plate of tube VI to the first grid of tube V- 2 by resistance-coupling, including plate load resistor R-4, coupling condenser C--3 and grid leak R-B. The far side of resistor R-l is connected to a filter condenser C2 and through a. filter resistor R-5 to a positive plate-current supply-bus l4 leading from an intermediate terminal, for example a volt terminal, of a high potential battery B, through one arm of a double pole switch S'2, the negative terminal of which is connected to ground through the other arm of the switch 8-2. In this position the switch 8-5 also connects the plate of tube V-2 to the grid of the triode section of V-3 by a resistance coupling including plate load resistor Rlll, coupling condensers 0-8 and C33 and grid leak R-39. The far side of resistor R-lfl is connected to a filter condenser C| 8 and through a filter resistor R-Q to the positive plate-current supply bus It. The potentiometer R--46 acts as an audio frequency gain control While the condenser C:':33 acts as a gain control coupling capacitor. Also, the switch 8-5 in this, the audio listening position, maintains the screen grids of tubes V-l and V2 connected to the high potential supply bus I4 through resistors 4 R,5, R-36 and R9,R,3'|, respectively. The plate circuit V-3 is coupled to the input circuit of the push-pull amplifier V-4 through the transformer T'2, the plate circuit passing through the primary of the transformer and a resistancecapacity filter R-l3. C-li. A push-pull output diode input of V3.

terminal of the diode load-resistor R,38 is made transformer T-3 couples the amplied output of tube V to the output jack J--l for reception through suitable receiving means not shown, and which may be of any known or other suitable type preferably a high quality head-telephone set. To prevent unnecessary loud noises in the head set of the operator during the transmission of a signal from the transmitter circuit, the plate circuit of the output amplifier tube Vl is connected to receive its power supply from bus l4 by way of a normally closed contact (back-contact) I5 on the keying relay l3 of the transmitter. From the foregoing it will be seen that with the circuits and apparatus elements in the condition shown in the drawing, the system functions as an audio listening device.

In listening either by audio or super-audio it is necessary to adjust both the super-audio gain control R-JS and audio gain control R-li. Control R.45 regulates the bias on the input tube V--l while R-46 controls the gain of the last two stages. A little experience will enable the sound operator to arrive quickly at the best adjustment of these two controls.

The receiver connected for audio reception as shown in the drawing operates as an audio amplifier passing all audible frequencies above 1,000 cycles per second. Underwater sounds in this range consist of propeller noises, noise from auxiliaries, wave noise and other natural noises in the water. The last two sources are undesirable and place a lower limit on the strength of sound from the first two sources that can be heard. It will be obvious that no sounds will be discerned from propellers or auxiliaries if their signal strengths are so small as to be masked by the general background of noise. Propeller noise in the audible frequency range from 1,000 to 10,000 cycles per second is characterized by a hissing sound, which often occurs broken up in such manner that the rhythm of the propeller can be detected.

Super-audio listening.-For reception of signals on superaudio frequencies, the listening band change-over switch S--5 is turned to move its indicating handle to the dotted line position SF, to rotate the five contact segments counterclockwise and establish the following connections for the receiver circuit. The connection of the plate of Vl is switched from the high resistance plate-load resistor R--4 to the plate tuned-reactance load C-4, Ir| tuned in the present instance to a band of frequencies about 1.5 kilocycles wide centered at the resonant frequency. 24 kilocycles, of the Rochelle salt crystals used in the transducer. Similarly the connection of the plate of V2 is switched from the high resistance plate-load resistorcondenser couple Rl0, C32 to the plate tuned-reactance load Cl0, L--2 tuned to substantially the same band of frequencies as the couple (3-4, L-l, and connected on the plate side through capacitor C9 to the Connection from the upper through R-IZ, R--| I the upper left hand switch segment, capacitor C8, potentiometer R-li and capacitor C-33 to the grid of V3. At the same time the two lower segments of switch S5 disconnect the screen grids of Vl and V--2 from the high resistance grid resistors R36 and R--3'| to the lower resistance screen grid resistors R-3 and R 8, respectively, to adjust'the screen-grid voltages to the increased plate current due to the substitution of the low resistance reactance plate-load for the high value plate-load resistors.

The receiver thus connected uses the tubes !-l and V-2 as a superaudio amplifier passing a band of frequencies of about 1.5 kilocycles wide F of V3, V and push-pull transformers 'I'-2 and T3, is preferably designed to pass all frequencies above 300 cycles per second. With this method of listening the audio signal output is roughly proportional to the square of the signal voltage. If, however, the local oscillator V-5, by closure of switch S-4, is put into operation, it will impress a strong signal on the diode detector of V3 along with the signal due to propeller noise, and the output will be roughly proportional tothe signal voltage. This condition is highly desirable especially when listening to weak signals. In the present embodiment of the invention the local oscillator is tuned a little oil? the above mentioned center frequency of 24 kilocycles, preferably about 23.2 kilocycles.

Supersonic listening is characterized by pronounced propeller rhythm, decided directional properties and low background noise, because of an absence of water-wave and auxiliary noises. In order to obtain the bearing of a noise source the directional transducer is rotated backward and forward until the position of greatest intensity is found which position, using a transducer having a diaphragm of about seven inches, has been found to give the hearing within two degrees, if care is taken to keep the gain low, for low gain tends to favor directional discrimination.

Since supersonic listening brings out the propeller rhythm very distinctly, a little listening experience will allow one to gain much information concerning the noise source. For instance, it is not difllcult to determine the number of propellers, the number of blades on each propeller, and the revolutions per minute. These data should allow the listener to form a fair estimate of the size and speed of the vessel. More experience will allow one to classify the type of vessel being heard by the quality of the propeller noise.

Echo ranging.-For echo ranging the transmitter portion of the system shown on the upper part of the diagram is brought into use. This comprises in general a twin-triode tube V--6 connected with auxiliary components to operate as a multivibrator pulse-frequency oscillator controlled by a trigger tube V-1 and an associated time-constant circuit through a relay to give intermittent signal pulses or bursts of oscillations. A pair of relay, gas tubes V8 and V9, triggered by' the oscillations from the multivibrator tube V6, alternately discharge storage condensers C-'26 and C21 through the primary winding of a transformer T4 for shock excitation of a tuned oscillating circuit formed by the secondary and a capacitor C29. A normally open contact IS on the relay I3 maintains connection of the oscillating circuit with the electrosonic transducer during a signal pulse. In the present embodiment of the invention, the tubes Consequently, if this band of ,I, 8, and 9, are of the "strobotron" type, a coldcathode, gas-filled tube having two control grids termed an inner grid and an outer grid the inner grid being the one nearest the cathode.

The time-constant circuit for the trigger tube J of the outer grid to that voltage whereupon the tube substantially instantaneous y discharges capacitor C2i and a capacitor -30 previously charged and maintained charged from the positive 270-volt terminal of the high potential battery B through the energizing winding of a keying relay l3. This brings the anode and outer grid of the tube to a low voltage extinguishing the tube. Current now passin through the energizing winding of relay 13 to charge condenser 0-30 energizes the relay to open contacts I! and i and close contacts l6 and i1, and maintain such condition of the contacts for a given period of time determined by the capacity of the condenser C-BO and the electrical and mechanical constants of the relay. Closure of contact ll maintains positive current supply to the plates of the multivibrator tube V-B from the supply bus it through plate resistors R2& and R.25. The tube V-S operating as a multivibrator applies tri gering impulses to the inner control grids of the relay tubes V-8 and V-9, alternately, by Way of coupling capacitors 0-25 and 0-28 respectively. This effects an alternate discharging of the storage capacitors C-26 and C--2'| from their upper plates to round through the primary winding of transformer-T4 by way of the plate circuits of tubes V-8 and V-9 respectively. Each capacitor discharges substantially instantaneously followed immediately by extinguishment of its associated tube. ducting condition of their associated tubes C--26 is charged through resistor R-3i, and C21 through resistor R-SZ by current from the positive '2'70-volt terminal of the high potential battery B. Thus, during operation of the multivibrator the secondary of the transformer T-4 and the transducer ID are shock excited at a number of shocks per second equal to the frequency of the multivibrator, the transducer projecting a signal consisting of pulses or trains of high frequency compressional waves at a pulse frequency equal to the frequency of the multivibrator. In the present embodiment of the invention the signal length may be one-seventh of a second, the pulse frequency an audible frequency of 400 per second and the frequency of the waves makin up the trains or pulses, a superaudio frequency of about 24 kilocycles per second.

For efficient operation the primary of the transformer T-4 should resonate with the capacitor C-28 or C-2'I at twice the resonant frequency of the tuned secondary and transducer. Because the contacts i2 and I5, are open during the sending of the signal, the outgoing signal produces no noise in the headphones of the listener. As the charge of capacitor C--3Il proceeds. the current passing through the winding. of relay l3 decreases until after a predetermined lapse 01 time it drops to a point where the relay During non-conreleases its armature opening contacts is and i1 and closing contacts I! and II.

The first noise heard is that of the reverberations, which arise from numerous discontinuities in the water near the transducer. Reverberations are always present but are worse at some times and places than at others. They die down in a time determined by the gain setting of the receiver and the existing water conditions. For best results the gain must be adjusted so that the reverberations will be very weak when the echo arrives. This means that, in general, the nearer the target the lower the gain should be.

As an aid in overcoming the interference due to reverberations a special control is provided marked "noise suppressor" on the drawing, and which comprises an adjustable potentiometer R-48 controlling the effectiveness of an automatic time-volume-gain system. This system comprises a condenser C22 connected in series with the full winding or other resistance element of the. potentiometer R-48 across the terminals of capacitor C-2l in the transmitter circuit, the adjustable center tap of the potentiometer being connected to the input control grid of the second amplifier tube V2 through the grid leak resistance R--6 of that tube by replacing what would ordinarily be the ground connection to such grid leak. In operation, after the substantially instantaneous discharge of capacitor C--2i through tube V-i, the capacitor C22 starts to discharge into C-2l at a rate retarded by the high resistance of the potentiometer. During the recharging of C-Zl retarded by resistors 12 -20 and Rl8, current flowing in a direction from ground through R-48 to the negative plate of C22 decreases to zero as the voltages of 0-22 and C2i approach equality after which C22 again charges with a reversal of current through R--B8. Thus upon discharge of C2| there is a drop in potential between the grounded side of R--48 and its center tap tending to make the grid of V2 more negative gradually changing to one tending to make the grid less negative, the degree of change depending in part upon the adjustment of the center tap of R-fl8 and the contribution to effective grid bias supplied by the resistor R-8.

Because this operation starts at the beginning of each signal transmitted, it is possible to find a setting for the center tap, marked noise suppressor on the drawing, at which the initial reverberations may be materially suppressed without diminishing the intensity of the echo.

The echo of the signal received through transducer l0 amplified through Vl and V-2 and detected and amplified through V3 and V-4 is received by the listener as an audible tone of the shock-frequency of 400 cycles per second. The time interval between signals can be varied by adjustment of the variable resistor R--20 through movement of the Range indicator which may be any known or other suitable form of indicating control element preferably graduated in yards. The range of keying interval is preferably in the neighborhood of one-fourth to three seconds.

In making a range determination the range indicator is tuned to lengthen the interval between signais to where there will be an appreciable separation between the reception of the echo from the target and the reverberations following a succeeding signal transmission. after which the indicator is-turned back to reduce gradually the time interval between transmissions until the desired echo of a signal is all but in known manner, and noting the resulting variations in reception.

Where it is desirable to measure ranges greater than possible with the range indicator the auto-' matic keying system is rendered ineffective by closure of switch S--3, and control of the trigger tube V--l by the hand key K established by inserting the plug P in the jack J-Z. With this connection, closure of the key will complete a discharge circuit for capacitor C20- through 10,000 ohm resistor Rr22. Current flowing from ground through R-22 to the lower or negative plate of the capacitor renders the inner gridof V--l negative with respect to ground and the outer grid being positive relative to ground due to dropping resistor R'2I a difference in potential is established between the grids suficient to fire the tube. Thus, each time the key K is depressed a signal will be transmitted. For these long ranges sufiicient accurac may beobtained by timing the interval between transmission and reception of the echo with a stop watch allowing 800 yards for each second of elapsed time.

For a more definite disclosure of the particular embodiment of the invention here illustrated diagrammatically in the drawing, a list of the electrical constants of some of the important components used is presented as follows:

Inductance elements L-l and L-2, variable inductor, 80 mh. nominal inductance. L-3 variable inductor, 80 mh. nominal inductance, tapped at 2.6 mh.

Transformer T-4; toroidal wound powdered iron core. mary, 3 turns of 116-strand No. 3'7 Litz. ondary, 55 turns of 29-strand N0. 37 Litz.

Relay Relay l3. Coil turns 60,000. Resistance 12,000

ohms.

Pri- Sec- Vacuum tubes V--l 6SJ7 pentode V2, GSK'Z pentode V3 and V5, 6SQ7 diode-triode V4, 6SL'7-GT dual triode V6, 6SN'7-GT dual triode V--|. V-8 and V9, SN4 strobotron cold cathe ode.

While one specific embodiment of the invention hashereinbeen described for the purpose of disclosure, it is to be understood that the invention is not limited to such specific embodiment, but contemplates all such modifications and variants thereof as fall fairly within the scope of the appended claims.

The invention described herein may be manu- I factured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon or therefor.

What is claimed is:

1. Means for measuring the distance to an,

object comprising a transducer, a tuned exciting circuit therefor, a plurality of electron tubes normally in a non-conducting state and connected in multiple to said transducer exciting circuit whereby flow of current through either tube will energize said exciting circuit, pulse control means alternately rendering said tubes conducting in rapid succession to produce a series of successive pulses, means determining the number of pulses in a group, means intermittently operating the pulse number-determining means, means varying the frequency of said intermittent operation, receiving means connected with the transducer for receiving echoes of said pulses, and means inhibiting reception of both incident and echo pulses during excitation of the transducer.

2. Means for measuring the distance to an object comprising a transducer for projecting and receiving wave energy pulses and tuned energizing circuit therefor, a plurality of gas filled tubes normally non-conducting and including said energizing'circuit in their output circuits, energy storing means associated with each tube and controlled by its associated tube for shock excitation of said energizing circuit, means for individually triggering said tubes in rapid succession, trigger control means intermittently rendering said triggering means effective for a given duration of time, means varying the interval of time between said effective periods, receiving means connected with the transducer for receiving echoes of wave ener y pulses projected by said transducer, and means controlled by said triggercontrol means inhibiting complete operation of said receiving means.

3. Means for measuring the distance to an object comprising a transducer for projecting and receiving wave energy pulses and tuned energizing circuit therefor, a plurality of gas filled tubes normally non-conducting and including said energizing circuit in their output circuits, energy storing means associated with each tube and controlled by its associated tube for shock excitation of said energizing circuit, means for individually triggering said tubes in rapid succession, trigger control means intermittently rendering said triggering means effective for a given duration of time, means varying the interval of time between said effective periods, receiving means connected with the transducer for receiving echoes of wave energy pulses projected by said transducer, and means operable with said trigger control means to inhibit reception of said signals during each intermittent period of repeated shock excitation.

4. Means for measuring the distance to an object comprising a transducer, a, plurality of gas filled tubes normally non-conducting, exciting means for the transducer responsive to the passage of a pulse of current through any of said tubes to excite said transducer to transmit a pulse of wave energy, a plurality of means for storing energy each associated with the anode circuit of one of said tubes, means for charging said storage means independently of said exciting means, a control grid for each tube, means for applying voltage pulses to said grids in rapid succession to cause the discharge of said energy storing means through the transducer exciting circuit in rapid succession.

5. Means for measuring the distance to an object comprising a transducer, a transformer having primary and secondary windings, a capacitor, said capacitor and secondary winding forming a circuit resonant at the resonant frequency of the transducer, a source of voltage, a storage condenser, a gas discharge tube controlling the discharge of the condenser through the primary winding of the transformer and normally non-conducting, means for intermittently rendering said tube conducting/to discharge the condenser through said resonant circuit to repeatedly shock excite the latter at a given frequency, means for detecting and amplifying radiant energy received by said transducer, means for intermittently simultaneously rendering said first mentioned intermittent means effective and said detecting and amplifying means ineifective for a given duration of time, and means for varying the frequency of said second intermittent action.

6. Means for measuring the distance to an object comprising a transducer, a plurality of gas discharge tubes independently controlling conduction of energizing current to said transducer, sequence firing means firing said tubes in repeated sequence, timed electrical switching means rendering said sequence-firing means operative for a given period of time, receiving means, said switching means operativelyconnecting said transducer with the discharge tubes to the exclusion of the receiver during operation of the sequence firing means, and operatively connecting the transducer to the receiver to the exclusion of the discharge tubes during non-operation of the sequence firing means, means intermittently operating said switching means, control means for said intermittent means for varying the intervals between operations of said switching means at will, and means variable with variation of said intervals to indicate distance.

7. An echo ranging system comprising-a transducer, a tuned energizing circuit therefor, a. pair of gas filled tubes having their output circuits connected in multiple to said tuned circuit for controlling shock excitation of said circuit, each tube having a control electrode, a pair of storage condensers, one for each tube, for supplying current for the output circuit of its tube, a multivibrator having each of its alternate output circuits operatively connected with one of said control electrodes for alternately triggering said tubes, electrically operated switching means controlling said multivibrator, automatic periodic control means intermittently energizing said switching means, continuously variable adjusting means for varying the periodicity of said intermittent energization of the switching means, a receiving circuit, said switching means connecting said transducer with said tuned circuit to the exclusion of the receiver during energization of the multivibrator and to the receiver to the exclusion of the tuned circuit during nonenergization of the multivibrator, and indicating means operated in unison with said adjusting meansgraduated to indicate the distance to the object when adjusted to a periodicity just short enough to initiate energization of the multivibrator for the transmission of. a signal after the echo of the preceding signal is received from the object and before receipt of the trailing edge of the echo whereby continued adjustment until the echoes become extremely short but distinct will give a correct reading.

8. Means for measuring the distance to an object comprising a transducer, a tuned circuit for'the transducer, a pair of discharge tubes independently controlling conduction of shock exciting current to said tuned circuitfor energizing the transducer to project a pulse of wave energy, a wave-energy receiver, a multivibrator having each of its alternate output circuits operatively connected each with one of said discharge tubes for alternately triggering the latter to effect recurring shock excitations of the transducer, electrically actuated switching means alternately connecting said transducer with said tuned circuit and said receiver, and connecting the multivi-brator with a source of operating current concurrently with connection of the transducer with the tuned circuit, and means variable to vary the period of said switching means and to indicate distance.

9. Means for measuring the distance to an ob- J'ect comprising in combination a transducer for projecting and receiving wave energy, a wave energy generating circuit, a plurality of discharge tubes having their output circuits connected in common to said generating circuit, control means rendering said tubes conductive in sequence repeatedly for a given period of time, timing means variably determining the interval between operations of said control means for said given periods of time, wave energy receiving means, means switching the-transducer from the receiver to the generating circuit during operation of the control means, and from the generating circuit to the receiver during intervals be-' tween operations of the control means and means variable with variation of said intervals between operations of said control means to indicate distance.

\ HORACE M. TRENT.

THOMAS F. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

